Microstructure Evolution and Mechanical Properties of Laser Welded Dissimilar/Similar Joints Between Medium‐Mn Transformation‐Induced Plasticity Steel and DP980/22MnB5 Steels

Abstract

In this article, the microstructure and mechanical properties of the Fe–0.31C–6.86Mn–3.53Al steel and DP980 and 22MnB5 steel dissimilar/similar joints by fiber laser welding are studied. Based on experimental results, fusion zone (FZ) of transformation‐induced plasticity (TRIP)‐welded joint mainly consists of 77 vol% martensite and 23 vol% ferrite. The FZ of TRIP‐DP980 and TRIP‐22MnB5 welds mainly consist of martensite. The hardness profile of weld cross‐section exhibits significant asymmetry, and softening zones hardness of TRIP‐DP980 and TRIP‐22MnB5 accounts for 82% and 64% of DP980 and 22MnB5 base materials (BM), respectively. However, no softening zone is observed on TRIP steel side, primarily due to the lack of martensite in TRIP BM. The tensile results showed that welding efficiency of TRIP‐TRIP reached 99%, but elongation of welded specimen is only 50% of TRIP BM due to the high hardness and brittleness of FZ region. TRIP‐DP980 and TRIP‐22MnB5 joints did not fail in softening zone, because the constraint stress is generated on both sides of softening zone to inhibit the plastic deformation in softening zone during tensile process. The tensile stress is distributed on the surface of tensile specimens and concentrated in BM on the side with low yield strength (YS), resulting in the final fracture.